Filled, biaxially oriented, thermoplastic film having preferential shrinkage and method of making such film

ABSTRACT

a filled, biaxially oriented, void-containing thermoplastic film suitable for making heat-shrinkable bands is provided having shrinkage on heating to 100° C. of greater than 5%, which shrinkage in turn is at least 5% greater than the shrinkage in a direction perpendicular thereto. 
     A process for preparing this film with its preferential shrinkage is provided including the steps of: 
     (a) melt-blending a C 2  -C 10  α-monoolefin polymer and at least 20 weight percent inert filler, based on the total weight of polymer and filler; 
     (b) forming a film from the melt blend; 
     (c) cooling the film to a temperature below the melting point; 
     (d) biaxially stretching the film at least about twice its original forming dimensions in mutually perpendicular directions while the film temperature is above the line-drawing temperature and below the polymer melting temperature, until the film has at least about 30% voids; 
     (e) cooling the film to room temperature; and 
     (f) post-stretching the biaxially stretched film in a selected direction at a temperature below 100° C. to an extent that provides the above-mentioned preferential shrinkage in the filled film.



